1) Field of the Invention
The invention relates to an electromechanical energy converter for generating electric energy from mechanical movements, with at least one bending bar that is clamped to a deflectable holder at a fastening point and that can be deflected from a neutral position transversely to the longitudinal extension of the bending bar relative to the fastening point along a trajectory with an free end area separate from the fastening point, whereby a deflectable part of the bending bar is connected to the holder by at least one deflectable bridge part spanning the bending bar for the purpose of creating a mechanical prestress on the bending bar oriented in an essentially longitudinal direction to the bending bar, with a setting mechanism for setting the prestress transferred from the bridge part to the bending bar, and that is connected to the bending bar by at least one electromechanical conversion element used for converting mechanical kinetic energy into electric energy. Movements can specifically include vibrations and/or jolts.
2) Discussion of the Prior Art
This type of energy converter is disclosed in Hu, Yuanttai et al. “A piezoelectric power harvester with adjustable frequency through axial preloads,” Smart Materials and Structures 16 (2007), pages 1961-1966. It has a bending bar unilaterally clamped to a holder with a square cross-section that can be elastically deflected in relation to its extension plane with its free end which is separated from the holder. The bending bar has a metal central layer arranged on its extension plane that is coated on its upper and lower side with a piezoelectric layer that runs parallel to the central layer. The holder is excited via a sinusoidal mechanical vibration towards the bending bar extension plane. The vibration causes the free end of the bending bar separated from the holder to elastically deflect to the bending bar extension plane relative to the holder. While deflecting the bending bar, an electrical potential is generated on the piezoelectric layers that feeds an electrical load, like e.g. an electronic microsensor.
To set the bending bar resonance frequency, the central layer has a passage hole in its center that spans the length of the bending bar and is drilled through by a screw that is screwed to the holder via its thread and whose screw head is in contact with the free end of the bending bar. With the help of the screw, the bending bar can be bolted in the axial direction in order to generate a mechanical prestress on the bending bar. With the help of the prestress, it should be possible to change the bending bar resonance frequency and adjust it to the vibration frequency. This should produce a higher efficiency conversion of vibrations into electric energy. With this type of prestress generation, however, only a relatively small amount of electric energy is converted from the mechanical vibration energy, particularly in broadband mechanical exciting vibrations and large exciting amplitudes.
The object is therefore to create an electromechanical energy converter of the aforementioned type with which an efficient conversion of mechanical vibration energy into electric energy can be achieved.